Heretofore, a digital video camera is known as a recording apparatus that shoots a subject, compression encodes moving image data thus obtained, and records the compression encoded moving image data to a recording medium, for example. In recent years, recording media used in such a recording apparatus have shifted from conventional magnetic tape towards disk media, semiconductor memories, and the like that are superior in terms of random accessibility and high access speeds. However, disk media and semiconductor memories generally have low-cost performance relative to storage capacity compared with magnetic tape. Thus, moving image data needs to be compression encoded with higher efficiency when using a disk medium or a semiconductor memory as a recording medium.
Digital video cameras that handle high definition (HD) video having greater information volume are also becoming more widespread given the expected high image quality. Higher efficiency compression encoding of moving image data is also desired from this viewpoint. MPEG-2 is the compression encoding system normally used for compression encoding moving image data with high efficiency.
Further, in recent years, higher efficiency compression encoding systems have been developed following further improvements in recording time to recording media and the increased need for lower bit rate encoding for mobile terminals with limited recording capacity. The H.264|AVC method is one of these. While requiring more operations for encoding and decoding in comparison to the conventional MPEG-2 and MPEG-4 methods, the H.264|AVC method is known to realize high encoding efficiency. Note that hereinafter “H.264|AVC method” will be abbreviated as “H.264”.
With H.264, various devices have been tried in order to raise encoding efficiency. Variable block size motion compensation is one example. This involves subdividing a macroblock (encoding block) constituting a unit of coding to form macroblock partitions (motion compensation blocks), and performing motion compensation in units of motion compensation blocks. With H.264, using variable block size motion compensation enables more accurate motion compensation in comparison to a conventional compression encoding system such as MPEG-2 that performs motion compensation with a single block size. An “encoding apparatus” proposed in Japanese Patent Laid-Open No. 2006-135734 is given as an exemplary invention that adaptively uses variable block size motion compensation.
However, with H.264, making encoding block size selectable as a result of variable block size motion compensation led to an increase in operation load for determining block size. That is, a motion vector search process needs to be performed for all motion compensation blocks that can be set with respect to an encoding block to be encoded, and an optimal block size selected. In view of this, it has been proposed to use information acquired when an image targeted for encoding is shot to reduce the amount of operations related to block size selection, as a way of determining an appropriate block size as simply as possible (e.g., see Japanese Patent Laid-Open No. 2006-254370)
With H.264, as noted above, a large amount of operations are required to perform motion vector searches and determine a motion compensation block division method, in order to perform motion compensation block segmentation resulting from variable block size motion compensation. Thus, a processor capable of extremely fast operations is required, particularly in the case where real-time encoding is performed such as with the above digital video camera, leading to an increase in device cost and power consumption.
Also, with the configuration of Japanese Patent Laid-Open No. 2006-254370, the camera unit needs to output information acquired when an image is shot to the encoding unit, and a mechanism is required on the encoding unit side for inputting and processing the information supplied from the camera unit during encoding.